Facebook has a billion users -- and they're about to start seeing hashtags, you know, #these #things. The practice of putting a pound symbol before a key word or phrase or acronym began on Twitter, when one guy, Chris Messina, suggested that Twitter allow them.
On August 25, 2007, Messina wrote up his proposal and posted it to his blog. Here's how he framed it. "I do think that there is certainly some merit to improving contextualization, content filtering and exploratory serendipity within Twitter," he said. "This is a rather messy proposal to that effect."
While people around him were talking about creating official "groups" on Twitter, Messina said he was "more interested in simply having a better eavesdropping experience on Twitter." So, looking around the web landscape at the time, which was quite different, he came up with a simple system that drew on preexisting conventions to create new functionality within Twitter. He imagined that each hashtag would create a (temporary) channel, analogous to an IRC (Internet Relay Chat) channel. Here's his condensed set of arguments for creating this new convention:
it is easily accessible adapting current Twitter syntax and convention, it's easy to learn and lightweight, it's very flexible and entirely folksonomic and works with people's current behaviors, rather than forcing anyone to learn anything radically new. It also keeps the interface aspects to a minimum (as I'll soon explain), invents little by borrowing from age old IRC conventions also adopted by an existing web application and, from what Britt said so far, actually works consistently on cell phones (whereas, for example, the star key does not).
Now, the rest of his proposal goes into a lot more detail, and what he initially envisioned was more robust than what Twitter actually implemented. But wow, was Messina onto something. Hashtags have gone to become an integral part (perhaps too integral a part) of many people's Twitter experiences. And now Facebook, the largest social network on the planet, is going to adopt them.
The history of any invention is complicated, as Messina's foundational post details, but this is one case in which some individual human being -- in the right place at the right time with the right contacts -- came up with something new and watched the whole (online) world adopt it. That's pretty amazing when you think about it.
Update: Wired's Sonal Chokshi reminded me that Messina didn't actually name the hash tag. The closest he came was, "To join a channel, simply add a tag hash (#)" in his suggested usage. The honor for the name goes to Stowe Boyd, who Tweeted on August 25, "I support the hash tag convention."
Eventually people got rid of the space, and "hashtag" was born. Ben Zimmer has all the details.